GE 90-30 PLC - Manual (Page 105)

C
C-4 TCP/IP Ethernet Communications User’s Manual - August, 1997 GFK-1084B
MAC Addresses
It is recommended that you use the default MAC address given by the factory, however,
you may override that default with a MAC address of your own choosing with the
Station Manager CHPARM MACADDR command (See GFK-1186.)
Each byte of the MAC Address is an 8-bit binary number. Thus, the 12-digit hex address
is really a 48-bit binary number. The typical MAC Address shown above is represented
as a binary number as follows:
Byte 1 2 3 4 5 6
________ _________ _________ _________ _________ _________
Hex 0 8 0 0 1 9 0 0 5 3 1 2
Binary 0000 1000 0000 0000 0001 1001 0000 0000 0101 0011 0001 0010
Another characteristic that is important, especially for multi-vendor networks, is the
order of address-bit transmission on the physical medium. MAC Addresses are
transmitted in ascending byte order, with the least significant bit of each byte
transmitted first.
The example above is shown including bit transmission order as follows:
Byte 1 2 3 4 5 6
________ _________ _________ _________ _________ _________
Hex 0 8 0 0 1 9 0 0 5 3 1 2
Binary 0000 1000 0000 0000 0001 1001 0000 0000 0101 0011 0001 0010
Bit Order 8765 4321 ...9 |
| MSB of the MAC
LSB of the MAC Address-first bit transmitted Address-last bit
transmitted
If you assign your own MAC Addresses, there are 2 bits of the 48-bit address that you
must set according to the instructions that follow:
H Bit 1 in Byte 1 must always be a 0 to indicate an individual station rather than a
Group address.
H Bit 2 in Byte 1 must be a 1 to indicate that the address is locally administered. (In the
typical default MAC Address shown above, bit 2 in Byte 1 is a 0 indicating that it is a
globally administered address).
H All other bits can be set as desired as long as all stations on the network have unique
addresses.
An example of a locally administered MAC Address is shown below.
Byte 1 2 3 4 5 6
________ _________ _________ _________ _________ _________
Hex 0 2 0 0 0 0 0 0 0 1 0 0
Binary 0000 0010 0000 0000 0000 0000 0000 0000 0000 0001 0000 0000
Bit Order 8765 4321 ...9 |
| MSB of the
LSB of the MAC Address-first bit transmitted MAC Address-last
bit transmitted
If you must change the Station MAC Address, check with the person administering your
network to make sure that you select an address that fits into your local administration
scheme.